Traditional weight machines are either plate loaded, where the user mounts the desired amount of weight plates on the machine manually, or weight-stack loaded, where the user selects the desired amount of weight from a weight stack using a removable pin. Both have their drawbacks.
While the plate-loaded machines allow smooth operation and a wide variety of load to be applied, even allowing the use of load increments as small as two and a half pound plates, it requires locating the various increments of the proper weight plates in a sometimes busy and disorganized weight room. Also, the plate-loaded machines require the user to load and unload the machine, which presents an injury hazard and wastes energy of the user better reserved for the actual exercise movement performed on the machine.
The weight-stack loaded machines are convenient, but most often only allow relatively large increments of weights (mostly 10 pounds) to be selected using the pin. Some weight-stack loaded machines have supplemental weights to allow for application of smaller increments of weights, but often require the actuation of a second weight selection structure for the supplemental weights. The weight-stack loaded machines typically have tall profiles. Also, the weight-stack loaded machines utilize tubular columns along which the weights displace. This arrangement results in relatively high friction generation and weight movement that is less smooth than plate-loaded machines.